1. Field of the Invention
The present invention relates to a die for molding disc substrates that is used when disc substrates, for recording information are molded.
2. Description of the Related Art
A die for molding disc substrates is comprised of a stationary die and a movable die, between which a cavity is formed when both are aligned with each other. Then, as shown in FIG. 3, a stamper 3 for transferring information to molded disc substrates is attached to a surface 2a of a specular plate 2 in at least one of the dies by an inner circumferential stamper holder 4 and an outer circumferential stamper holder 5, which support an inner circumference and an outer circumference of the stamper 3, respectively. The inner circumferential stamper holder 4 has a cylindrical shape and it is provided with an outer circumferential surface 4a that is formed around its outer circumference, and a claw member 4b that is formed around the outer circumferential portion of a cavity forming surface or one end face of the inner circumferential stamper holder 4 to support the stamper. Then, in the inner circumferential stamper holder 4, said outer circumferential surface 4a abuts against a side surface 3a of a center opening of the stamper 3 and said claw member 4b supports an inner circumferential portion 3b. However, because the stamper abutting surface 4c of the outer circumferential surface 4a of the inner circumferential stamper holder 4 abuts against the side surface 3a of the center opening of the stamper 3 as described above, the outer circumferential surface 4a is gradually worn away due to reasons such as friction with the side surface 3a of the center opening of the stamper 3 as the molding operation is performed repeatedly. Then, as the abrasion of the outer circumferential surface 4a of the inner circumferential stamper holder 4 progresses, the stamper 3 deviates from the center of the inner circumferential stamper holder 4, which may result in defects in the molded disc substrates. Therefore the conventional inner circumferential stamper holder 4 must be replaced about every month due to the abrasion of the stamper abutting surface 4c of the outer circumferential surface 4a and, as a result, costs are increased.
On the other hand, a technique for preventing the abrasion of the inner circumferential stamper holder 4 as set forth in Japanese Unexamined Patent Publication No. H10-302328 is well-known. FIG. 8 of Japanese Unexamined Patent Publication No. H10-302328 mentioned above shows that a back of a fastening claw member 127 of a stamper fastening member 126, which corresponds to the inner circumferential stamper holder 4 in this specification, is coated with a metallic compound to prevent the abrasion of said fastening claw member 127. However, the coating over the back of the fastening claw member 127 is not effective for preventing the deviation of the stamper 3 from the center of the stamper fastening member 126 and it does not result in increased service life of the stamper fastening member 126. Rather, there is a problem in that the coating over the backside of the fastening claw member 127 makes it difficult to finish the back of the fastening claw member 127 after the coating is applied. Further, FIG. 9 of Japanese Unexamined Patent Publication No. H10-302328 mentioned above shows that a second protective layer such as lubricating oil is formed on a contact portion where a stamper 111 makes contact with a stamper fastening member 125 in the thickness direction of an optical disc. However, as a matter of fact, the second protective layer shown in FIG. 9 of Japanese Unexamined Patent Publication No. H10-302328 is not significantly effective for preventing the abrasion of the stamper fastening member 125 from progressing. Moreover, it is difficult to apply the lubrication oil to an outer circumference of said stamper fastening member 125 uniformly and maintain the uniformly applied layer for a long time and, further, there are problems in that a fixing position of the stamper is likely to deviate from the center and the lubrication oil may leak out to the surface of the stamper if too much lubrication oil is applied.